Dry separating table, a separator and equipment for the compound dry separation with this table

ABSTRACT

The present invention discloses a combined dry sorting bed, the sorting bed is arranged with an inclination, and the inclination between the longitudinal extending of said bed surface and horizontal plane is from −2° to +4°, and the inclination between the lateral extending of said bed surface and horizontal plane is from 0° to +15°. By reasonable setting of the angle of inclination, the material being separated spiral overturn continuously on the sorting bed under the influence of the rising air currents and the force of vibration, with the result that the light material in the upper layer is separated under the influence of weight. The material is sorted for many times during the circularly movements, the product with different content of ash can be obtained. This invention also relates to a combined dry sorting device that comprises frame, sorting bed, vibrator and air supply device. This invention further relates to an apparatus for separation that comprises a feeding device, an air supply and dedusting device and a separating device, the above mentioned sorting bed is used in the sorting device and apparatus, therefore different products with vary quantity of ash are generated according to the gravity of material, and the accuracy of separation is improved.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage application under 35 U.S.C. §3.71 of international stage application PCT/CN2003/000768, filed Sep.12, 2003, which claims priority of Chinese patent application serialnumber 03261328.8, filed May 18, 2003.

FIELD OF THE INVENTION

This invention relates to a dry sorting bed, a combined dry sortingdevice with the sorting bed and an apparatus for separation, which is asolid sorting apparatus and is particularly suitable to be used to thesorting of coal from waste-rock and pyrite, and the sorting of solidparticle intermixture whose densities are different from each other.

BACKGROUND OF THE INVENTION

It is well known that the dry sorting apparatus used in industrialproduction at home and abroad are mainly pneumatic jig and air table.The method of using air to replace water as sorting medium has alreadybeen eliminated through selection gradually for its poor sorting effect,low production capacity and a large amount of wind power demand.

An adverse current sorting apparatus was disclosed by American Graham &Troman Co., Ltd in Volume one of the book Coal-beneficiation Techniquepublished in 1988. It's a kind of air table, whose bed surface isrectangular and is provided with an inclination of 10°. The longitudinalvibration device makes the bed surface move longitudinally and the bedsurface adopts a perforated plate. A blower fan sends wind under theplate at a constant wind speed and pressure. The upward flowing airflowmakes the materials on the bed surface sorted in layers and then theheavier waste-rock falls onto the perforated plate through the table andmove upward and slantways along the bed surface effected by eccentricto-and-fro movement. In this way, the lighter coal emerges at the upperlayer on the table and is pushed by the fed-in materials to move alongthe downwards-slanting bed surface. In nature, it's a kind ofair-fluidized bed. The sorting is completed on the bed surface at atime. The float coal is discharged at a time, but it is easy for finegrain waste-rocks to drop in the coal. Therefore, the sorting effect isvery poor, the production rate is low and the demanded wind power isvery large. There is also another kind of dry type shaking table, whichneeds no wind power and depends on the helical motion of the materialsto make the materials sorted in layers. In this way, the coarse grainsstay at the upper layer and the fine grains stay at the lower layer. So,the sorting effect is poor because it is made according to the densityof the materials.

A combined type sorting method was published in 1990s, which adopts theself-born medium (i.e. the fine grain coal contained in the raw coal tobe sorted) and air to form air-solid two-phase medium for sorting; whichutilizes mechanical vibration to sort the materials time after time bymaking them roll spirally; and which makes the most of the buoyancyeffect of the interaction between grains generated by the graduallyincreased density of the materials on the table to sort the materials.Under such a condition that the materials are made to roll spirally onthe bed surface of the sorting apparatus, the combined action of thevibratory force and the ascending air is utilized to make the materiallayers on the table incompact and make the mineral grains layeredaccording to density. Under the effect of gravity, the materials whosedensity on the surface layer is low are delaminated. While this actionis repeated, the materials are sorted time after time. By delaminatinglayer upon layer, several kinds of products are produced whose ashcontents are from low to high, until the waster rocks and iron pyritesare discharged. Then, sorting is made by making use of the fine grainmaterials in the fed-in raw coal (called self-born medium) and upwardflowing gas to form air-solid two-phase medium. In this dispersionmedium with a certain density, the low-density materials emerge upwardand the high-density materials sink. Then, pure waste-rock product isobtained by making use of the buoyancy effect generated by theinteraction of the heavier grains to make the coal grains mixed in thewaste-rock layer emerge continuously.

CN2101532 and CN2314850 respectively disclosed the above combined typeof dry sorting apparatus, which are applicable to sorting material ofsolid particle admixture, in which the density of the solid particles isdifferent. The sorting apparatus consist of a vibrator and a sorting bedhung from the frame to form a vibration bed. The vibration bed isprovided with lattice bars according with the direction of the motion ofmaterials. The bed surface between lattice bars is equably provided withvertical wind ports connected with the air chambers. A slantingbackboard is attached to the back of the sorting bed surface. Affectedby the vibratory force and upward flowing gases, the materials movespirally and are sorted into layers according to density. Throughcirculatory sorting time after time, the low-density materials areseparated from the high-density materials.

However, the following problems exist in the sorting beds disclosed byabove two patents:

Firstly, the above patents didn't disclose the obliquity of the bedsurface of which the lateral angle and longitudinal angle directlyaffect the sorting effect. If the lateral angle is too small, thethickness of the materials on the table will increase and the sortingspeed of the coal on the surface will decrease. If the lateral angle istoo large, the vibration speed of the high-density materials at thebottom will decrease, or may not move at all, which will ruin thesorting process. If the longitudinal positive angle (waste-rockdischarging end is lower than material feeding end) is too large, thewaste-rocks and coal will gather into the waste-rock discharging port.If the longitudinal negative angle (waste-rock discharging end is higherthan material feeding end) is too large, the waste-rocks will move at anexcessively low speed and accumulate too much on the table to ruin thesorting process. Therefore, it is extremely important for the bedsurface have a rational obliquity. Secondly, the functions of theparallel lattice bars on the bed surface include: (i) guiding thehigh-density mineral grains to move to the waste-rock channel; (ii)increasing the speed of the high-density mineral grains at the bottom ofmaterials on the bed surface to move to the waste-rock end, which ispropitious to the increasing of the processing rate of the sorting bed;(iii) sorting function to a certain extent. The low-density coal at thetop of the materials on the bed surface can cross over the lattice barsto move to the material discharging side and the high-density materialsat the bottom of the materials on the bed surface will be the held up bythe lattice bars and can only move along the lattice bars to thewaste-rock end, which increases the sorting accuracy. Therefore, anappropriate height and obliquity of the lattice bars is very importantto the effect of sorting. Thirdly, the shape of the bed surface issquare pentagon and the proportion of the width of the feeding side tothe length of the bed surface is 4:10, resulting in shorter sortingtime, easier for waste-rocks to drop in the float coal and moredifficult for sorting accuracy to be increased. Fourthly, the abovepatents didn't provide the degree of the obliquity between the backboardand the bed surface, but the angle of the backboard guides the materialsto move spirally, which is very important for the separation of lightmaterials. Fifthly, vibration form of the bed surface is electromagneticvibration or low amplitude inertial force vibration, which isn'tpropitious to the sorting of the materials whose partial sizes arecomparatively large and which moves the materials at the bottom of thematerials on the bed surface at a low speed and it is very difficult toincrease the production capacity.

OBJECT OF THE INVENTION

Therefore, the first object the present invention is to provide acombined dry sorting bed, of which the sorting accuracy is comparativelyhigh and the production capacity is comparatively large, to overcome theshortcoming of the obliquity of the sorting bed surface of the prior artso that the sorting accuracy and efficiency accordingly can beincreased.

The present invention further overcomes the irrationality of the latticebars setting angle on the sorting bed surface of the prior art andselect rational lattice bar obliquity to improve the sorting quantity.

This invention further overcomes such problems that the sorting bed istoo narrow, the breadth length ratio is too small, the initial sortingtime is too short and the sorting accuracy is low in the prior art.

The second object of the present invention is to provide combined drysorting advice with the above sorting bed of this invention that canovercome the limitation of the prior art and is provided with a rationalobliquity, aspect ratio, lattice bar obliquity and backboard obliquityto improve the sorting accuracy.

This invention is further provided with rational vibratory strength toimprove sorting accuracy and production capacity.

The third object of present invention is to provide apparatus forseparation that can integrate sorting with de-dusting, blowing andfeeding, whose sorting bed overcomes the shortcomings of the sorting bedof the prior art.

SUMMARY OF THE INVENTION

To realize above object, the present invention firstly provided acombined dry sorting bed, comprising the bed surface that isapproximately right-angled trapezoid, whose hypotenuse is the materialdischarging side of the sorting bed. A discharging baffle is provided inthe material discharging side. A backboard that guides the materials toroll upwards is set at the right angle side opposite to the materialdischarging side. The wider side of the bed surface is the feeding sideand the narrower side is waste-rock discharging end. A plurality of airsupply ports is positioned on the bed surface. The sorting bed arrangedwith an inclination, the inclination (“α”) between the longitudinalextending of the bed surface and horizontal plane is from −2° to +4° andthe inclination (“β”) between the lateral extending of the bed surfaceand horizontal plane is from 0° to +15°.

For the longitudinal angle of the bed surface, the positive angle refersto the obliquity formed by the waste-rock discharging end below thehorizontal plane and the negative angle refers to the obliquity formedby the waste-rock discharging end above the horizontal plane. For theinclination between lateral bed surface and horizontal plane, thepositive angle refers to the obliquity formed by the materialdischarging side below horizontal plane.

In order to make the materials sorted time after time and make thehigh-density materials move towards the waste-rock discharging end toimprove the sorting accuracy, strip lattice bars are provided on the bedsurface at intervals and in parallel. The lattice bars extend from thematerial discharging side, toward the direction of the backboard andwaste-rock discharging end to a position where there is some space apartfrom backboard, the space constitute the waste-rock channel accordingly.According to experiments, the angle formed by the lattice bars and thefeeding side is from 25° to 45°, preferably from 32° to 37°, which leadsto best sorting accuracy.

When sorting, the backboard should be provided with a rationalobliquity. In this way, the materials to be sorted can be made by themechanical vibration to do rational spiral rolling motion to improve thesorting accuracy and efficiency accordingly. The angle between thebackboard and the bed surface is from 30° to 90°, preferably from 45° to60°.

The shape of the bed surface is a right angle trapezoid, with thematerial discharging side being oblique and the bed surface becomesnarrower and narrower from the feeding side to waste-rock dischargingend. In this way, the materials layer on the bed surface from thefeeding side to the waste-rock discharging end will have a uniformthickness.

The ratio of length of the feeding side to the longitudinal length ofthe bed surface is from 50% to 80%, preferably from 60% to 70%. Thewidth of the bed surface should be chosen rationally in order to let thematerials have reasonable sorting time each time they are sorted andimprove the sorting accuracy. Rationally choosing the longitudinallength of the bed surface can improve the sorting efficiency and avoidwaste.

The height of the discharging baffle is higher than ½ of the maximumgrain size of the maximum density of sorted material to prevent thehigh-density materials from sliding in the light-density materialsduring the vibration of the sorting bed.

The waste-rock discharging end is provided with a waste-rock gate, whichis a gate of board and can be opened and closed. The function of thegate is that when the waste-rock content in the raw coal is low,partially closing the waster rock gate can form a thicker waste-rocklayer on the bed surface and prevent the coal grains from dropping inthe waste-rock products.

The present invention also provided a combined dry sorting device,comprising frame, sorting bed, vibrator and air supply device. Thesorting bed and vibrator are hung in the frame, the vibrator isconnected with the sorting bed and the air supply device is connectedwith the bottom of the sorting bed. The sorting bed comprises a rightangle trapezoidal bed surface and the hypotenuse of the right angletrapezoid is the material discharging side of the sorting bed. Thematerial discharging side is provided with a discharging baffle, and theright angle side opposite to the discharging side is provided with abackboard to guide the materials to roll upwards. The wider side of thebed surface is the feeding side and the narrower side is the waste-rockdischarging end. A plurality of air supply ports is positioned on thebed surface, and the sorting bed is placed slantwise, the inclination“α” between the longitudinal plane and horizontal plane of the bedsurface is from −2° to +4°, and the inclination “β” between the lateralplane and horizontal plane is from 0° to 15°.

Strip lattice bars are provided on the bed surface at intervals and inparallel. The inclination between the lattice bars and feeding side isfrom 25° to 45°, preferably from 32° to 37°. The inclination between thebackboard and bed surface is from 30° to 90°, preferably from 45° to60°. The ratio of the length of the feeding side of the bed surface tothe longitudinal length is from 50% to 80%, preferably from 60% to 70%.

The air supply device comprises the air chambers located under andconnected with the sorting bed. The blower fan is connected with the airchambers through the airline and the joints between the airline and airchambers are flexible. There are more than one air chambers and each oneis provided with a valve to control the air quantity of each air chamberrespectively.

The sorting bed and vibrator are hung in the frame by overhangingdevice. The overhanging device comprises a steel cable, one end of thesteel cable is connected to the top of the frame and the other end isconnected to the adjuster in the frame by passing through the travelingblock disposed on the sorting bed and the crown block in the frame. Theupper end of the steel cable is provided with damping springs.

The vibrator is connected with the backboard of the sorting bed and thevibration passes through the center of gravity of the sorting bed andforms a 20° inclination with the bed surface along the across (lateral)direction of the bed surface.

The present invention further provides an apparatus for separation,which comprises a feeding device, an air supply and dedusting device anda separating device, in which:

(a) feeding device comprises belt conveyer, surge bin and vibratingfeeder;

(b) separating device comprises frame, sorting bed, vibrator anddischarging device;

(c) air supply and dedusting device comprises air chambers, blower fan,airline, dedusting fan, dust hood, cyclone dust collector and bag typecollector.

The belt conveyer is located at the upper part of the surge bin and thebottom of the surge bin is connected with the vibrating feeder.

The sorting bed and vibrator are hung in the frame by the overhangingdevice. The vibrator is connected with the sorting bed and the materialdischarging device is under the material-discharging end of the sortingbed.

The outlet of the blower fan is connected with the air chambers at thebottom of the sorting bed. The dust hood is located at the top of thesorting bed and one of the outlets at the top of the dust hood isconnected with the cyclone dust collector and is connected with theinlet of the blower fan through the airline. The inlet of the bag typecollector is connected with another outlet of the dust hood and theoutlet at the top of the bag type collector is connected with the inletof the dedusting blower fan.

The sorting bed comprises bed surface, backboard and discharging baffle.The bed surface is approximately right angle trapezoid, whose hypotenuseis the material discharging side of the sorting bed. The dischargingbaffle is located at the material discharging side of the bed surfaceand the right angle side opposite to the material discharging side isprovided with a backboard to guide the materials to roll upwards. Thewider base side of the bed surface is the material discharging side andnarrower base side is the waste-rock discharging side. The waste-rockgate is located at the waste-rock discharging side of the bed surface.The bed surface of the sorting bed is provided with lattice bars atintervals and in parallel. A plurality of air supply ports is set on thebed surface. The sorting bed is placed slantwise and the inclination “α”between the altitude direction of the trapezoid (longitudinal) and thehorizontal plane is from −2′ to +4° and the inclination “β” between thedirection vertical to the altitude of the trapezoid (lateral) and thehorizontal plane is from 0° to 15°.

The material-discharging device comprises discharging sluices of floatcoal; middling coal and waste-rock and is located under the separatingdevice. An adjustable platform trap door is positioned in thedischarging sluice of the material discharging device. The adjustableplatform trap is a transversely laid gate shape plane table and itswidth is a little less than the width of the material-receiving trough.It is installed in the middling and waste-rock receiving trough and itsbottom end is at the center of the material discharging port. A handleis provided outside the material-receiving trough. Turning the handlecan change the position of the platform trap door to adjust the materialreceiving width and control the product quality. A belt conveyer is setat the bottom of each material-discharging sluice.

The air chamber is integrated with the bed surface under the bedsurface. Each air chamber is flexibly connected with air supply line anda valve is provided at the inlet of every air chamber respectively.

The outlet of the dedusting blower fan is connected with the air exhaustpipe.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic drawing of the side view of the combined drysorting bed of the present invention.

FIG. 2 is a schematic drawing of the top view of the combined drysorting bed of the present invention.

FIG. 3 is a schematic drawing of the front view of the combined drysorting device of the present invention.

FIG. 4 is a schematic drawing of the side view of the combined drysorting device of the present invention.

FIG. 5 is a schematic drawing depicting the front view of the apparatusfor separation of the present invention.

FIG. 6 is a schematic drawing depicting the side view of the apparatusfor separation of the present invention.

FIG. 7 is a schematic drawing depicting the top view of the apparatusfor separation of the present invention.

In which, Sorting bed 100, Bed surface 101, Waste-rock discharging end102, Backboard 103, Feeding port 113, Discharging side 104, Dischargingbaffle 105, Feeding side 106, Waste-rock channel 107, Waster rock door108, Lattice bar 109, Air supply port 110, Wearable rubber bed surface111, Frame 200, Vibrator 300, Electric motor base 301, Thrust sheet 302,Air supply device 400, Air chamber 401, Blower fan 402, Air-supply line403, Rubber tube 404, Air door 405, Slag tripper 406, Flange 407,General air door of blower fan 408, overhang device 500, Steel cable501, Traveling block 502, Fixed block 503, Adjuster 506, Damping spring507, Material discharging device 600, Material receiving trough 601,Belt conveyer 602, Adjustable platform trap door 603, Waster rock exit604, Middling exit 605, Float coal exit 606, Dust hood 702, Exit 702,Cyclone dust collector 703, Bag-type dust collector 704, Air duct 705,Dust blower fan 706, Pastern-shaded sealing 707, Exhaust duct 708, Backblower fan 709, Belt conveyer 11, Surge bin 12, Vibrating feeder 13.

DETAILED DESCRIPTION

The foregoing and other objects, features and advantage of the inventionwill become apparent from the following description of preferredembodiments with reference to the accompanying drawings.

Example 1

Referring to FIGS. 1 and 2, which shows the combined dry sorting bed 100with bed surface 101. The bed surface 101 is in a shape of a trapezoid,and the ratio of the feeding side length to the length of the bedsurface 101 is 60%. The material discharging side 104 is the bevel edgeof the trapezoid. There is a discharging baffle 105 on the materialdischarging side 104 and it is set at several places and the height maybe adjusted up and down. The lower base line of the right-angledtrapezoid is the feeding side 106, the upper base line of the trapezoidis waste-rock discharging end 102, and the backboard 103 leading thematerial to roll upward is located on the right-angle edge. The heightdirection of the said trapezoid is defined as the longitude direction ofbed surface 101, and the direction normal to the height is the across(lateral) direction. On the bed surface, lattice bar 109 is set atintervals and in parallel. There are some air supply ports 110 on bedsurface 101, and the sorting bed is laid slantwise. The angle “α” formedbetween longitude direction of the bed surface and the horizontal planeis 0°, and the angle “β” form by the across direction of bed surface andthe horizontal plane is 10° (not shown in the drawing).

In this embodiment, the ratio of the feeding side to the lengthwisestrength of the said bed surface 101 is 60%, so that bed surface 101 maybe provided with adequate length and width and the time for each sortingand times of sorting may be more reasonable so as to improve sortingaccuracy and efficiency.

In order to improve sorting accuracy and increase sorting times, latticebars 109 are set on the bed plate at intervals and in parallel, whichextends from material discharging side 104 to the direction of backboard103 and the waste-rock discharging end 102 and to a position where thereis some space apart from backboard 103. Therefore, this space forms awaste-rock channel 107, and an inclination of 32° is formed between thelattice bar 109 and the material discharging side 106. The heights ofthe lattice bars between the feeding port and waste-rock discharging endare respectively 120 mm, 100 mm, 80 mm, and 60 mm, and the others areall 40 mm. The thickness of bed layer at the feeding port is more than200 mm, and the higher lattice bars prevent large waste-rocks from beingmixed into the coal, so that they are separated as early as possible.The descending of the lattice bar height may cause the medium or smallblocks of waste-rock to separate, and the height of the lattice barsbehind the material discharging side is all 40 mm, which does not affectthe rolling of the material to be sorted. When sorting massive raw coalwith 40% waste-rock content, if there are no high lattice bars thecontent of waste-rock in the float coal is 7%, and while there are highlattice bars, the content of waste-rock is 1%, and without any massivewaste-rock.

As the inclination between backboard 103 and bed surface 101 is 45°,under the resistance of backboard 103 and the force of vibration, thebulk material is provided with a reasonable helical angle, which isadvantageous to separation of the light materials.

In the meantime, the air supply port 110 on bed surface 101 had betterbe tapering so as to avoid any blockage, and wearable rubber bed surface111 (not shown in the figure) should be covered on bed surface 101 so asto extend the life of use for the bed surface.

In order to prevent the mineral grains of high density near the materialdischarging side from dropping into the light materials during thevibration of the bed surface, which is slanting downward, the saiddischarging baffle 105 is arranged in several sections, whose height canbe adjusted. Properly adjusted, the baffle has these functions: to peeloff the material of lower density on the surface, to control thethickness of the material layer on the bed surface, and to preventsingle waste-rock from entering into the cleaned coal. In this Example,the height of the discharging baffle is about ¾ (at least ½) the largestgrain diameter of the waste-rock to be sorted.

At the waste-rock discharging end of sorting bed, there is a waste-rockdoor 108. In the case that there are only a few waste-rocks in raw coal,partially shut the waste-rock door 108, then a thicker layer ofwaste-rock on the bed surface may be formed at waste-rock dischargingend, so that coal grains are kept away from entering into the waste-rockproducts.

In practice, the vibrating direction of this sorting bed is at aninclination of 20° between the across direction and the bed surface. Theslanting angle of the bed surface of this sorting bed is arranged asdownward slanting along the across direction of the bed surface, and asapproximately horizontal along the longitude direction in which thematerial moves. Under the vibration of the bed surface and the windpower below the bed surface, the material executes a helical motionlaterally along the bed surface. And under the action of gravity, thematerials of lower density on the surface slide down along thematerial-discharging side 104 and are peeled off by the dischargingbaffle. Furthermore, longitudinally the bed surface is approximatelyhorizontal, which ensures not only that the materials of high densitythat passes from feeding side 106 through waste-rock channel 107 to thewaste-rock end 102 have certain speed, but also that the materials oflower density are prevented from entering into waste-rock product.According to the content of waste-rock in raw coal, the longitudeinclination may be adjusted. When the content of waste-rock in raw coalis the largest (such as more than 20%), in order to adjust the movingspeed of waste-rock, the longitude inclination of the bed surface shouldbe adjusted to a positive one, so that the waste-rock may slide downunder the vibrating inertia force and gravity. However, the strip ofwaste-rock should be ensured with an adequate length to reach a dynamicequilibrium. When the content of waste rock in raw coal is small (suchas less than 10%), in order to avoid any coal in waste-rock product, thelongitude inclination of the bed surface should be adjusted to anegative one, so that the waste-rocks have to climb and their movingspeed may be reduced. Partially shut the waste-rock door when necessaryso as to ensure the length of the waste-rock. The way to adjust thelongitude inclination of the bed surface is the same as that to adjustits lateral obliquity. Modifying the length of the 2 wire ropes near thewaste-rock end can change the longitude inclination of the bed surface.

Compared with wind power coal preparation technology in the prior art,this invention has the following advantages:

The sorting bed of the present invention is set in a reasonableobliquity, under the vibration force of bed surface and the action ofthe wind power, the sorted material vibrates at an inclination of 20°between across direction and bed surface, so that the material isaffected by the upward vertical component force and the horizontalcomponent backboard force. When the material move in the backboarddirection under horizontal component force, upward wind power and upwardcomponent force, the light material is thrown upward; and guided by thebackboard, the materials begin to move and roll helically in acrossdirection along the bed surface. As the obliquity between the bedsurface and the across direction is 10° downward, it is easy for thelight material to be peeled off under the action of gravity. And thenthe material is discharged along the material discharging side, which isslanting downward. Furthermore, the longitude direction of the bedsurface is approximately horizontal; on the one hand, the materials oflower density that pass from the feeding side through waste-rock channelto waste-rock end may be provided with certain speed, on the other handthe materials lighter than waste rocks may be prevented from enteringinto waste-rock product.

In this Example, by reasonably designing the aspect ratio of the bedsurface and increasing the length of the feeding side, the initialsorting time of raw coals is ensured and the sorting accuracy isimproved, and as the width from feeding side to waste-rock dischargingend is getting narrower and narrower, an even thickness of the materialon bed surface is also ensured. Because the feeding side of thisinvention is wider than that of the existing sorting bed, the time ofeach sorting is longer, which ensures an adequate sorting time andsorting accuracy. Along with the constant discharging of the sortedlight materials, the retained material on the bed surface is gettingfewer and fewer. The width of the bed surface is narrowed down, so thematerial layer on bed surface may keep a certain thickness, so as toimprove the sorting accuracy and sort products of various densities fromlow to high.

The height and obliquity of lattice bars should be chosen reasonably.The bars should be kept parallel and form an inclination of 32° with thefeeding side. As the vibrating direction is normal to the direction ofbackboard, the lower layer of waste-rock close to the bed surface needsa vertical component force, which is caused by the obliquity of thelattice bar, to lead the waste-rock to move toward the waste-rock end. Alarge obliquity will also cause a large vertical component force,improve the vertical moving speed, and increase the separating speed, sothat the treating ability of the sorter is correspondingly improved.Whereas, if the obliquity is too large, the vibrating inertia force willget too large a resistance from the lattice bar, and the effect of thevertical component force will be reduced instead. Therefore, anappropriate obliquity of the lattice bar is needed, so that the materialmay move to the backboard direction along the lattice bar. The lightmaterial is thrown up and rolls upward. The lattice bar leads thematerials of high density to move to the waste-rock end, those of lowerdensity are sorted for several times when they roll through the latticebars because of gravity. Furthermore, the flute between the lattice barsforms a waste-rock layer on the bed surface and that is advantageous tosorting.

In this embodiment, the obliquity of the backboard has been chosenreasonably, and the inclination between the backboard and the bedsurface of the sorting bed is 45°, which makes the light material, whichis rolling upward along the backboard and being led and driven by thebackboard, is thrown up to the material discharging side. There is anelectric motor frame and an electric motor outside the backboard. Theinner side of the backboard leads the material on the bed surface toroll upward and form a kind of helical motion.

The wearable rubber bed surface has a certain friction coefficient thathelps to improve the conveying speed of the material at the bottom layeron the bed surface, and keeps the bed surface from wear and tear. Theback-tapering air supply port may avoid any blockage, and the diameterand space between two air supply ports not only ensure an incompactlayer on bed surface but also keep the fine coal grain on the bedsurface from dropping.

There are several adjustable discharging baffles on the materialdischarging side of the bed surface. The excellence is that thethickness of the layer may be controlled by adjusting the height of thebaffle, and massive waste-rock may also be prevented form entering intocleaned coal. And after adjusting the height of the baffle, the sortedproduct may be distributed evenly along the material discharging side.

There is a waste-rock door at the waste-rock discharging end on the bedsurface. In the case that there are only a few waste-rocks in raw coal,partially shut the waste-rock door, then a thicker layer of waste-rockon the bed surface may be formed at waste-rock discharging end, so thatcoal grains are kept away from entering into the waste-rock product.

Example 2

It is different from Example 1 in the obliquity of bed surface 101: theangle between longitude direction of the bed surface 101 and thehorizontal plane is −2°, and that between the across direction and thehorizontal plane is 7°. The proportion of the feeding side to thelongitude length of bed surface is 50%. The inclination between thelattice bar and the feeding side is 40°, and that between the backboardand the bed surface is 60°. This Example is applicable for treatingmixed coals, where the content of waste-rock is more than 40%. When itis sorted, it is advantageous for the waste-rock to be discharged.

Example 3

The difference between this Example and Example 2 is in the obliquity ofbed surface 101: the inclination between the longitude direction of thebed surface 101 and the horizontal plane is +2°, and that between theacross direction and the horizontal plane is 1°. The proportion offeeding side to the longitude length of the bed surface is 70%. Theinclination between the lattice bar and the feeding side is 30°, andthat between the backboard and the bed surface is 45°. This Example isapplicable for treating mixed coals, where the content of waste-rock isless than 10%. When it is sorted, it is advantageous for improving thesorting accuracy and treating ability of cleaned coals.

Example 4

The difference between this Example and Example 3 is in the obliquity ofbed surface 101: the inclination between the longitude direction of thebed surface 101 and the horizontal plane is +4°, and that between theacross direction and the horizontal plane is 13°. The proportion offeeding side to the longitude length of the bed surface is 80%. Theinclination between the lattice bar and the feeding side is 45°, andthat between the backboard and the bed surface is 70°.

Example 5

The difference between this Example and Example 4 is in the obliquity ofbed surface 101: the inclination between the longitude direction of thebed surface 101 and the horizontal plane is +0°, and that between theacross direction and the horizontal plane is 3°. The proportion offeeding side and the longitude length of the bed surface is 65%. Theinclination between the lattice bar and the feeding side is 25°, andthat between the backboard and the bed surface is 30°. This Example isapplicable for treating raw coals of small grains, where the content ofwaste-rock is less than 5%.

Example 6

Referring to FIGS. 3 and 4, which show the combined dry sorting device,including sorting bed surface 100, frame 200, vibrator 300, airsupplying device 400. The sorting bed 100 and vibrator 300 are both hungon frame 200. Vibrator 300 is connected with sorting bed 100, underwhich there is air-supplying device 400. The sorting bed 100 is justthat described in FIG. 1-2. See the description of the three Examples ofsorting bed.

The sorting bed 100 and vibrator 300 are both hung on frame 200 byoverhang device 500, for which the steel cable 501 is connected with thetop of frame 200 at one end and with the adjuster 506 on the frame 200at the other end that passing by the traveling block 502 on the sortingbed and by the fixed block 503 on the frame 200. And there is a dampingspring 507 on the upper end of eth wire rope 501. By using theelectrical adjuster 506 on the overhang device 500, the length of thesteel cable 501 may be adjusted to change the transversal orlongitudinal inclination of the bed surface 101. The sorting bed isinstalled on the frame with a hanging structure, so vibration resistanceand energy dissipation are small. The base vibration is very weakbecause of the damping spring. Due to the combined use of the fixedblock and the traveling block, the stress of the wire rope is reduced.The transversal or longitudinal inclination of the bed surface may beadjusted through the electrical adjuster.

The shape of the bed surface 101 of the sorting bed 100 is about aright-angled trapezoid, of which the inclination “α” between thelongitude direction and the horizontal plane is 4°, and the inclination“β” between the cross direction and the horizontal plane is 12°. Thedischarging baffle 105 is on the discharging bevel edge of theright-angled trapezoid, and the feeding port 113 is on the feeding edgeon the lower base line of the right-angled trapezoid. Backboard 103 thatleads the material to roll upward is on the right angle edge oppositethe material discharging side 104, and a waste-rock door 107 is set atthe waste-rock discharging end on the upper base line of the trapezoid.Further more, there paved a rubber bed surface 111 over the bed surface101, on which there have been set a number of lattice bars 109 thatextends from material discharging side 104 to the direction of backboard103 and the waste-rock discharging end 102 to a position where there issome space from backboard 103. Therefore, this space forms a waste-rockchannel 107, and an inclination of 35° is also formed between thelattice bar 109 and the material discharging side 106. Some ports 110are set between the lattice bars on the bed surface. Below one side ofthe material discharging side of the bed surface 101 is materialdischarging equipment 600, including material receiving trough 601,which is below the discharging baffle 105. Inside the material-receivingtrough there is an adjustable platform trap door 603 that may beadjusted transversely. A belt conveyer (now shown in the figure) can beset below the material-receiving trough 601, which conveys the sortedproducts to designated places. By one side of the material dischargeedge of the bed surface, there are several material receiving troughswith adjustable platform trap doors. The quality of the dischargedproducts may be controlled by adjusting the platform trap door to changethe width of the received materials.

The air supply device 400 comprises an air chamber 401 below andintegrated with the sorting bed 100. The air chamber 401 is connectedwith the blower fan (not shown in the figure) through the air-supplyline 403. Air chambers 401 are respectively connected with air-supplyline 403. At the lower end of the air-supply line 403 there is a slagtripper 406, and the other end of the air-supply line 403 is connectedwith the blower fan (not shown in the figure) via a flange 407. Beingintegrated with the sorting bed, the air chamber is able to vibratetogether with the sorting bed. There may be several air chambers, andfor this Example, there are 3 air chambers, which are respectivelyprovided with an air door 405 controlling the air delivery of every airchamber. The slag tripper 406 may eliminate the float coal granulesleaking into the air duct from the bed surface.

Vibrator 300 is a double-vibration rectilinear electric vibrator that isintegrated with backboard 103 of the sorting bed 100 through electricmotor frame 301 and thrust sheet 302. Its vibrating direction is throughthe center of gravity of the sorting bed and in the across direction ofbed surface 101, with which a inclination 20° is formed. Adjusting theexcitation force of the electric vibrating motor, the swing of thesorting bed 100 may be changed. As the inclination between the vibratingdirection and the bed surface is 20°, not only are the materials in thebottom provided with an adequate motion velocity, but the motion of thematerials will not damage the waste-rock layer.

Over the sorting bed 100, there is a dust hood 701 and two coordinateexits 702, which are respectively connected with the dedusting device(not shown in the figure) to discharge purified air into the atmosphere.Around the dust hood 701 and to the sorting bed 100, there ispastern-shaded sealing equipment 707 to prevent outflow of the coal dustfrom the sorting bed.

When being sorted, the materials are sent into the feeding port 113 fromthe feeding machine 13 above the sorting bed 100 and then form amaterial layer on the bed surface. Air is sent into the air chamber 401in the bottom of the bed surface, and an upward airflow will then formthrough the airports 110 on the bed surface. By the combined action ofthe vibrating force and the upward airflow, the material layer on thebed surface will get incompact and the mineral grain will be delaminatedas per density. As the inclination between the vibrating direction andthe horizontal plane is 20°, the upward airflow makes the fine grains inthe raw coal float and form a mixed medium layer of gas and solid.Therefore, under the vibrating inertial force, the materials contactingwith the bed surface move from the discharging baffle 105 to thebackboard 103 along the lattice bar 109. Being resisted and guided bybackboard 103, the material roll upward and form a material layer of lowdensity on the surface. And with the effect of the gravitation, thematerials glide down to the discharging baffle 105, which peels off thefloat coal of the lowest density and drops them into thematerial-receiving trough 601. Most of the retained materials willcontinue to make shuttling movement for sorting. The bottom layer ofhigh-density material on the bed surface moves to the corner ofbackboard 103 and bed surface 101 and then moves to the waste-rockdischarging end through the waste-rock channel 107. Passing through thewaste-rock door 108, it is discharged into the waste-rock-receivingtrough 601. Being peeled off layer by layer, products of different ashcontent ranging from low to high are produced, and finally waste-rocksand sulfur iron ores of the highest density are discharged.

The combined dry sorting device has a simple structure and a uniquesorting principle. Compared with wind-driven coal sorting technology inthe prior art, it is provided with more advantages such as lessinvestment, lower production costs, higher sorting efficiency, lessenvironmental pollution, smaller land occupancy, stronger applicability,shorter construction period, and fewer maintenance times and so on.

Referring to FIG. 5-7, which shows an apparatus for the separation ofcoal that comprises a feeding device, an air supply and dedusting deviceand a separating device, in which,

The feeding device: comprising belt conveyer 11, surge bin 12, andvibrating feeder 13.

The sorting device: comprising frame 200, sorting bed 100, vibrator 300,and material discharging device 600.

The air supplying and dust collecting device: comprises air chamber 401,blower fan 402, air supply line 403, general air door 408, dust blowerfan 706, cyclone dust collector 703, and bag-type dust collector 704.

The belt conveyer 11 is located at the top of the surge bin 12, which isconnected downward with the vibrating feeder 13. The said sorting bed100 and vibrator 300 are both installed on frame 200 through an overhangdevice 500, as shown in FIG. 4. Vibrator 300 is combined by a vibratingmotor, which is connected with sorting bed 100 through electric motorbase 301 and thrust sheet 302. Material discharging device 600 islocated below the material discharging end of sorting bed 100. The exitof blower fan 402 is connected with air chamber 401 in the bottom ofsorting bed 100 through air-supply line 403. As shown in FIG. 4, as thissorting bed is the same as the one shown in FIG. 4. The air chamber 401is connected and integrated with sorting bed 100. The dust hood 701 islocated over sorting bed 100 and is connected through an exit on the topwith the cyclone dust collector 703, and it is also connected throughair duct 705 with the entry of blower fan 402. The other exit of dusthood 701 (or several exits may be set) is connected with the entry ofbag-type dust collector 704, of which the exit on the top is connectedwith the entry of dust blower fan 706. The exit of dust blower fan 706is connected with exhaust duct 708. On the upside of bag-type dustcollector 704 is back blower fan 709, and on air-supply line 403 infront of blower fan 402 is the general electric air door 408.

As shown in FIGS. 1 and 2, sorting bed 100 of this sorting unit includesbed surface 101, which is in the shape of a right-angled trapezoid. Onthe material discharge edge 104 on the bevel edge of the trapezoid,there are several discharging baffles 105, which are adjustable up anddown. The lower edge of the trapezoid is feeding side 106, and the upperedge is waster rock discharging end 102, where there is a waste-rockdoor 108. Backboard 103 guiding the material to roll up and down islocated on the right angle edge of the trapezoid. On the bed surface,there are lattice bars 109 leading the material to move. The heightdirection of the trapezoid is defined as the longitude direction of bedsurface 101, and the direction normal to the height is the acrossdirection. There are some air supply ports 110 on bed surface 101, andthe sorting bed is laid slantwise. The inclination “α” between thelongitude direction of bed surface 101 and the horizontal plane is from−2° to +4°, and the inclination (“β”) between across direction of bedsurface and horizontal plane is from 0° to +15°.

As shown in FIG. 3, the air chamber in this embodiment is connected withbed surface downward. Every air chamber 401 is connected with air-supplyline 403 through rubber tube 404, and in which there is set an air door405 respectively.

The material-discharging device 600 comprises material receiving troughsfor cleaned coal, middling and waster rock, and is below the sortingbed. In material discharging trough 601 there is an adjustable platformtrap door 603, and below the material-discharging trough 601 there is afloat coal exit 606, where there is a belt conveyer 602 to transportcleaned coal. Below the material-receiving trough 601 for middling andwaste-rock, there is waste-rock exit 604 and middling exit 605.

The operation principle of this embodiment is that the belt conveyer 11send the raw coal into surge bin 12, the vibrating feeder 13 controlsand evenly feeds the material into sorting bed 100; the fed-in raw coalform a material layer of some thickness on sorting bed 100 and getincompact under vibrating force and wind power and then is delaminatedas per densities. The float coal of lower density on the top layer ofthe material passes through the discharging baffle 105 and drop tomaterial-receiving trough 601 then to the float coal exit 606 andfinally to the belt conveyer 602 to be transported to outside. The layerof waste-rock and sulfur iron ore in the bottom of the bed surfaceconcentrates at the waste-rock end under vibrating inertia force and isdischarged through waste-rock exit 604. There is dust hood 701 on theupper side of sorting bed 100 and there are at least 2 coordinate exitsto collect the dust. There are 2 lines for coordinate dust collection:one is that the dusty gas is sent into cyclone dust collector 703 fromone exit of dust hood 701, then return back to blower fan 402 after thedust is removed, which then sends into each air chamber 401 through airduct 403 and therefore a shuttling movement is formed. This operatingline ensures a good sorting effect and there is less wear and tear forthe impeller of the blower fan. The other is that part of the dusty airand the air around the dry-way sorter enter into eth bag-type dustcollector 704 from the other exits of dust hood 701, then the filtratedpurified air is drained into the atmosphere through exhaust duct 708 bydust blower fan 706 under the bag-type dust collector 704, so that it isoperated under negative pressure and ensure that the operationalenvironment and the atmospheric environment will not be polluted. On thetop of bag-type dust collector 704, there is installed a back blower fan709 to clean up the coal dust on the filter bag.

The feeding may be controlled by the way adjusting the swing and theobliquity of vibrating feeder 13, and the longitude direction and acrossdirection degree of the sorting bed 100 may be controlled by the wayadjusting overhang device 500, so that the work efficiency and sortingeffect may be improved, and the air delivery of every air chamber, theexcitation force of vibrator 300, the height of material-dischargingbaffle 105, the width of waste-rock door 108 may be all adjusted and thedegree of adjustable platform trap door 603 in material-receiving trough601 may also be adjusted, and various raw coals may all be sorted withthe best effect.

The present invention may also be provided with electric control parts,including stepping-down starting cabinet, electric power distributioncabinet, and auto-control cabinet, all of which may achieve manual orautomatic linked control, automatic control in starting and shuttingdown, automatic alarm, shutting down resonance protection of the table,and the system running status indication and so on.

The apparatus of the present invention is provided with a simplestructure, a wide application range, and a high sorting efficiency. Itis easy and convenient to be operated and to be dismantled, transported,and installed. The air supplying and dust collecting part ensures that asmooth sorting operation of the combined dry-type sorting device andapparatus can be obtained, a clean working environment kept, dustcontamination prevented and a high efficiency of coal sorting and dustcollecting attained.

1. A combined dry sorting bed, comprising a bed surface that isapproximately right-angled trapezoid, wherein the hypotenuse of saidsorting bed is a material discharging side and wherein the materialdischarging side comprises a discharging baffle; a backboard for guidingmaterial to roll upwards is set at the approximate right angle side ofsaid bed surface opposite to said material discharging side, wherein afeeding side of said bed surface is wider than a waste-rock dischargingend of said bed surface; and, a plurality of air supply ports areprovided on said bed surface, wherein said sorting bed is arranged withan inclination, wherein the inclination between the longitudinalextension of said bed surface and horizontal plane is from −2° to +4°and the inclination between the lateral extension of said bed surfaceand horizontal plane is from 0° to +15°.
 2. The combined dry sorting bedof claim 1 wherein a plurality of strip lattice bars in parallel arepositioned at intervals on said bed surface, and said lattice barsextend from the material discharging side, toward the direction of thebackboard and waste-rock discharging end to a position where there is aspace apart from backboard, the space constituting the waste-rockchannel, wherein said bars each have a height, and wherein the heightsof said bars descend in turn from said feeding side to said waste-rockdischarging end.
 3. The combined dry sorting bed of claim 1 wherein theangle between said lattice bars and said feeding side is from 25° to45°.
 4. The combined dry sorting bed of claim 1 wherein the anglebetween said backboard and said bed surface is from 30° to 90°.
 5. Thecombined dry sorting bed of claim 1 wherein the ratio of length of saidfeeding side to the longitudinal length of said bed surface is from 50%to 80%.
 6. The combined dry sorting bed of claim 1 wherein the height ofsaid discharging baffle is higher than ½ of the maximum grain size ofthe maximum density of sorted material.
 7. The combined dry sorting bedof claim 1 wherein said waste-rock discharging end is provided with awaste-rock gate.
 8. A combined dry sorting device containing the sortingbed of claim 1 comprising a frame; a sorting bed; a vibrator; an airsupply device, wherein said sorting bed and vibrator are hung in theframe, said vibrator is connected to said sorting bed, and said airsupply device is connected to the bottom of said sorting bed, whereinsaid sorting bed comprises a bed surface that is approximatelyright-angled trapezoid with a material discharging side as thehypotenuse thereof; a discharging baffle extending along said materialdischarging side; a backboard for guiding the material to roll upwards,wherein the backboard is set at the right angle side of said bed surfaceopposite to said material discharging side, wherein a feeding side ofsaid bed surface is wider than a waste-rock discharging end of said bedsurface; and, a plurality of air supply ports provided on said bedsurface; wherein said sorting bed is arranged with an inclination,wherein the inclination α between the longitudinal extension of said bedsurface and horizontal plane is from −2° to +4° and the inclination βbetween the lateral extending extension of said bed surface andhorizontal plane is from 0° to +15°.
 9. The device of claim 8 whereinsaid air supply device comprises air chambers located under andintegrally connected with said sorting bed, wherein a blower fan isconnected with the air chambers through the air line, and wherein jointsbetween the air line and air chambers are flexible joints.
 10. Thedevice of claim 9 further comprising a plurality of air chambers, eachhaving an air valve to control air quantity.
 11. The device of claim 8wherein a plurality of strip lattice bars are positioned in parallel atintervals on said bed surface, wherein said lattice bars extend fromsaid material discharging side toward the direction of the backboard andwaste-rock discharging end to a position spaced from the backboard, toform the waste-rock channel, and wherein said bars each have a height,and wherein the heights of said bars descend in turn from said feedingside to said waste rock discharging end.
 12. The device of claim 11wherein an angle between said lattice bars and said feeding side is from25° to 45°.
 13. The device of claim 8 wherein an angle between saidbackboard and said bed surface is from 30° to 90°.
 14. The device ofclaim 8 wherein a ratio of length of said feeding side to thelongitudinal length of said bed surface is from 50% to 80%.
 15. Thedevice of claim 8 wherein said air supply port on said bed surface is inthe form of a reverse taper.
 16. The device of claim 8 wherein said bedsurface is covered with wearable rubber.
 17. The device of claim 8wherein said vibrator is connected to said backboard of said sorting bedand the direction of vibration is along an across direction of the bedsurface and passes through a center of gravity of said sorting bed, andforms approximately a 20° inclination with the bed surface.
 18. Thedevice of claim 8 wherein said sorting bed and vibrator are hungrespectively in the frame by an overhanging device, said overhangingdevice comprises a steel cable, wherein one end of said steel cable isconnected to a top of said frame, and wherein the other end is connectedto an adjuster in said frame by passing through a traveling blockdisposed on said sorting bed and a crown block in said frame, and saidupper end of the steel cable is provided with damping springs.
 19. Thedevice of claim 8 wherein a material discharging device is located undersaid material-discharging end of said sorting bed, and wherein saidmaterial discharging device comprises discharging sluices in which anadjustable trap door is provided.
 20. The device of claim 8 wherein adust hood is further provided over at least a portion of said sortingbed, said dust hood having at least two exits.
 21. An apparatus forseparation comprising a feeding device; an air supply; a dedustingdevice; and, a separating device, wherein said feeding device comprisesa belt conveyer, a surge bin and a vibrating feeder, wherein saidseparating device comprises a frame, a sorting bed, a vibrator and adischarging device, wherein said air supply and said dedusting devicecomprise air chambers, a blower fan, an air line, a dedusting fan, adust hood, a cyclone dust collector and a bag type collector, whereinsaid belt conveyer is located at the upper part of said surge bin and abottom of the surge bin is connected with said vibrating feeder, whereinsaid sorting bed and said vibrator are hung in said frame by anoverhanging device, said vibrator is connected with said sorting bed,and said material discharging device is located under saidmaterial-discharging end of said sorting bed, wherein an outlet of saidblower fan is connected with said air chambers at a bottom of saidsorting bed through said air line, wherein said dust hood is over atleast a portion of said sorting bed and one of the outlets at the top ofthe dust hood is connected with said cyclone dust collector and isfurther connected with an inlet of said blower fan through the air line,and wherein an inlet of said bag type collector is connected withanother outlet of said dust hood and an outlet at a top of said bag typecollector is connected with an inlet of said dedusting blower fan. 22.The apparatus of claim 21 wherein said air chamber is integrated withsaid bed surface under said bed surface, wherein each air chamber isflexibly connected with said air supply line and a valve is provided atsaid inlet of each air chamber.
 23. The apparatus of claim 21 whereinsaid material-discharging device comprises discharging sluices of finecoal, middling and waste-rock respectively and is located at a bottom ofsaid separating device, and wherein an adjustable trap door is providedin said material receiving trough.
 24. The apparatus of claim 21 whereinthe outlet of said dedusting blower fan is connected to an air exhaustpipe.
 25. The apparatus of claim 21 wherein said sorting bed comprises:a bed surface having a plurality of air supply ports; a backboard; and,a discharging baffle, wherein said bed surface is approximatelyright-angled trapezoid having a hypotenuse, wherein said hypotenuse issaid material discharging end, wherein said discharging baffle ispositioned in said material discharging end, wherein said backboardguides the materials to roll upwards and is set at a right angle side ofsaid bed surface opposite to said material discharging end, wherein afeeding side of said bed surface is wider than a waste-rock dischargingend of said bed surface, wherein said waste-rock end comprises awaste-rock gate, wherein said sorting bed has a first inclination and asecond inclination, said first inclination extending between alongitudinal extension of said bed surface and a horizontal plane, andthe second inclination extending between a lateral extension of said bedsurface and said horizontal plane, wherein said first inclination isfrom −2° to +4° and said second inclination is from 0° to +15°.
 26. Theapparatus of claim 25 wherein a plurality of strip lattice bars arepositioned in parallel at intervals on said bed surface, and saidlattice bars extend from said material discharging side toward thedirection of the backboard and waste-rock discharging end to a positionspaced from the backboard, the space comprising the waste-rock channelaccordingly, and wherein said bars each have a height, and wherein theheights of said bars descend in turn from said feeding side to saidwaste-rock discharging end.
 27. The apparatus of claim 26 wherein theangle between said lattice bars and said feeding side is from 25° to45°.
 28. The apparatus of claim 25 wherein the angle between saidbackboard and said bed surface is from 30° to 90°.
 29. The apparatus ofclaim 25 wherein ratio of length of said feeding side to thelongitudinal length of said bed surface is from 50% 80%.